The TODO list is on the web:
 http://caca.zoy.org/wiki/libpipi/research/filters
 http://caca.zoy.org/wiki/libpipi/research/gamut
 http://caca.zoy.org/wiki/libpipi/research/warping
 http://caca.zoy.org/wiki/libpipi/research/coolstuff

See also the libpipi tickets:
 http://caca.zoy.org/report/1